Quantum dots (QD) are semiconducting nanocrystals that have recently received a lot of interest because of their efficacy as fluorescent probes. They offer a significant increase in photostability and fluorescence lifetime compared to more traditional organic dye-based probes; however, some concern from their potential in vivo use due to their chemical composition and their nanoscale dimensions exists. Within this chapter, we discuss current knowledge about the fluorescence properties and pharmacological profile of quantum dots, showing how these characteristics can be altered after incorporation within previously established drug delivery systems for the formation of novel hybrid systems. The incorporation of therapeutic agents into such hybrid systems can further result in the construction of theranostic devices, namely, QD-based theranostics. Alternatively, conjugation of quantum dots to therapeutic moieties can be used as a scaffold for theranostic device design. This chapter will discuss the current progress in QD-based theranostics.